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The Science of Sleep: Unraveling Biology and Culture

The rate of insomnia in the U.S. is climbing, and with it, so too are a host of health problems blamed on inadequate sleep. Getting our eight or more hours per night has become a common concern and has encouraged a growing industry of sleep aids, such as pills, light blocking curtains, and glasses built to block blue light. But are the rules about getting the full eight hours a biological necessity or are they simply a cultural development?

Evidence for Preindustrial sleep patterns found in South America and Africa

Scientists studying cross-cultural sleep habits have exposed North Americans’ sleep biases, and blown apart the notion that a solid 8 hours is the norm. A team of researchers asked how many hours of sleep per day our preindustrial ancestors may have gotten, using modern-day indigenous Bolivians, Tanzanians, and Namibians as proxies. They found that sleep times in these communities averaged between 5.7 and 7.1 hours per night, as opposed to the prescribed 8 hours. Community members also do not experience some of the health complaints associated with poor sleep and inflammation, such as atherosclerosis, obesity, and high blood pressure.

Additionally, although it was assumed humans are biologically wired to take naps, the scientists refuted the hypothesis that hunter-gatherers (and hunter-horticulturalists in the case of Bolivian Tsimane) take regular siestas. Contrary to popular belief, the participants in this study did not go to sleep as soon as the sun set—they instead used firelight to stay up for more hours of activity, and tended to wake before sunrise.

As diurnal creatures, light profoundly affects our sleep patterns. The scientists noted that sleep cycles were in tune with daily temperature variations. Sleep onset appeared to coincide with falling temperatures, and awakening with rising morning temperatures. They suggested that difficulty falling asleep in industrialized nations may stem in part from climate control in houses, which keeps homes at a steady temperature.

Speaking of sleep disturbances, Bolivian (called Tsimane) and Namibian (called San) study participants did not even have a word for insomnia in their languages, and very few (1.5 – 2.5%) reported having regular sleep disturbances, in contrast to 10 – 30% rates of insomnia in industrialized countries.

The authors of the study think that these sleep patterns may be representative of the “natural,” biologically-determined human sleep patterns that would have existed before human migration from Africa, and certainly before industrialization. In other words, uninterrupted sleep a few hours after sundown, patterned from temperature fluctuations, with people rising before dawn after six or seven hours of sleep, is a normal sleep template. But can we take the patterns of these study participants as truly ‘natural’?

Sleep: The “messy block party”

This report sparked a reaction from the cultural anthropology student in me. I wondered about the scientists’ suggestion that preindustrial sleep patterns are primarily biological processes, since culture and biology are intricately intertwined. The idea that something as important for daily functioning as sleep would be devoid of cultural influence did not sit well. It was even more interesting considering that some of the scientists are biological anthropologists, who study human evolution and biological and social variation. So, I began to sift through cultural anthropology research to see if I could uncover more information about cultural sleep patterns.

I came across a study by Roger Ekirch on segmented sleep. Using archival data (including diaries, literature, and legal depositions), Ekirch found that pre-industrial sleep in Europe was biphasic—this means that in between two periods of sleep, many people would arise for a period of late night wakefulness, during which they might even get up to visit their neighbors. He, like the authors of the cross-cultural sleep patterns study, argued that this “biphasic” sleep was the natural heritage of pre-industrial peoples. Ekirch’s study opposes the research on Bolivian, Tanzanian, and Namibian hunter-gatherer sleep habits, which shows the “natural” pattern to be one solid block of sleep. The authors of the latter study argue that biphasic sleep in Europeans may be related to long European nights further from the equator.

Ekirch argues that this British engraving by Jan Saenredam from the late 1500’s is evidence of biphasic sleep patterns. See BBC for details | Wikimedia Commons

But the long nights nearer the poles may not be the only factor driving differences in sleep patterns. In fact, there are variations in sleep patterns in cultural groups living closer to the equator. For example, Botswana !Kung (related to the Namibian indigenous from the cross-cultural study) and Zaire Efe peoples wake multiple times per night to tend fires. As author Carskadon described it, “People stay up as long as something interesting—a conversation, music, dance—is happening and they participate; then they go to sleep when they feel like it” (p.79). Carol Worthman at Emory University detailed the “messy block party” of communal sleeping in non-Western communities, claiming that 25 percent of Indonesian Temiars and Sarawak Ibans may be awake and active during any one part of the night.

Biology and culture are complicated bedfellows

Cultural patterns of human behavior, including sleep, are fluid and change in the presence or absence of many factors, including whether or not there is something good on Netflix, or if one drinks coffee way too late in the day. Even if the authors of the cross-cultural sleep habit study consider hunter-gatherers as proxies for pre-industrial humans near the equator, can we extrapolate this data to include all equatorial human civilizations? Which ones, and during which time periods? There are no static, unchanging patterns of belief and behavior, as culture is enacted and transformed in everyday life. I question the concept of “natural” human sleep, and I wonder how to untangle the biological and social aspects of sleep habits.

Jennifer DeMoss is a doctoral candidate from the University of Georgia’s Anthropology and Integrative Conservation programs. She is currently in the field researching social relationships between people and landscapes within educational programs in the Nature Connection Movement. She uses tools such as GoPro cameras strapped onto her head to video social interactions as part of her research. When she’s not interviewing people, she loves to camp, practice primitive skills, carve spoons, and swim in spectacular northern lakes. You can contact Jen at jdemoss@uga.edu.